The present disclosure relates to footwear that results in reduced joint loading compared to common walking shoes currently available. In particular, the present disclosure relates to footwear having a flexible sole with a series of flexure zones positioned to correspond to primary joint axes. The footwear of the present disclosure thus approximates the characteristics of a bare foot in motion.
Osteoarthritis (OA) of the lower extremity in humans is related to aberrant biomechanical forces. Dynamic joint loading is an important factor in the pathophysiology of OA of the knee. The prevalence and progression of knee OA are reported to be associated with high dynamic loading. One standard parameter assessed as a marker of dynamic knee loading is the external knee adduction moment, a varus torque on the knee that reflects the magnitude of medial compartment joint loading. This moment is considered to be important because nearly seventy percent of knee OA affects the medial tibiofemoral compartment of the knee. The peak external knee adduction moment has been reported to correlate both with the severity and with the progression of knee OA. Consequently, strategies that effectively reduce loads on the knee during gait would be useful.
Biomechanical interventions aimed at reducing medial compartment loading, such as lateral wedge shoe orthotics have been investigated as therapeutic options. Insertion of lateral wedge orthotics into regular shoes can induce significant decreases in knee moments by up to 5% to 7%, in subjects with medial compartment knee OA. Furthermore, since the lower extremity joints are interrelated, alterations of mechanics at the foot, may not only affect knee loads but may have consequences at the other lower extremity joints.
Loading at the knees may be affected by altering the ground reaction force. The ground reaction force is the upward force exerted on a human body from the ground in opposition to the force of gravity. It is equal and opposite to the force the human body exerts through the foot on the ground. Because ground reaction forces are transmitted through the feet, such forces are influenced by footwear.
Prior studies of the effects of footwear on joint loading have been restricted to control subjects without OA, and have demonstrated that even moderate-heeled shoes increase peak knee torques. In addition, one study suggested that common walking shoes may result in increased knee loads in normal individuals, but these effects were attributed to differences in walking speeds while wearing shoes. One study evaluated hip loads in a patient who had an instrumented prosthesis inserted at the time of joint replacement for hip OA. The instrumented prosthesis included a force transducer for obtaining force measurements. By obtaining direct force measurements from the force transducer of the prosthesis, the investigators were able to demonstrate that there were no differences in hip loads among nearly 15 different types of shoes, but the hip loads were lower when the subject was barefoot compared to any of the footwear.
Walking barefoot significantly decreases the peak external knee adduction moment compared to walking with common walking shoes. An 11.9% reduction was noted in the external knee adduction moment during barefoot walking. Reduction in loads at the hip were also observed. Stride, cadence, and range of motion at the lower extremity joints also changed significantly but these changes could not explain the reduction in the peak joint loads.
Common shoes detrimentally increase loads on the lower extremity joints. Therefore, it is desirable to mitigate factors responsible for the differences in loads between footwear and barefoot walking as applied to common shoes and walking practices to reduce prevalence and progression of OA.